#define _CRT_SECURE_NO_WARNINGS 1
class Solution {
public:
    int takeAttendance(vector<int>& records) {
        int left = 0;int right = records.size() - 1;
        if (right == 0)return records[0] == 0 ? 1 : 0;
        while (left < right)
        {
            int mid = left + (right - left) / 2;
            if (mid == records[mid])left = mid + 1;
            else right = mid;
        }
        return records[left] == left ? left + 1 : left;
    }
};